This type of device heretofore employed is an EFG method (Edge defined Film fed Growth method), in which a molten liquid in a crucible, molten by a heater, is caused to raise up to the upper end portion of a die by the capillary action of a capillary tube disposed centrally of the die and the molten liquid is pulled up to the upper end face of the die, thereby manufacturing a single crystal of a configuration defined by the outward shape of the upper end portion of the die. The greatest feature of the EFG method is to guide the molten liquid up to the upper end portion of the die through utilization of the capillary action, as described above.
This method has an advantage such that a constant amount of molten liquid, which is substantially dependent on the wetting property between the molten liquid and the die, can be stably supplied to the solid-liquid interface, but this leads to such a defect that the above method is limited to only specific combinations of materials of the molten liquid and the die. That is, for the application of the EFG method, it is necessary that the materials of the molten liquid and the die satisfy both of two conditions that (1) they are wettable of each other enough to cause a sufficient rise of the molten liquid by the capillary action, and that (2) they do not chemically react with each other. In practice, however, combinations of materials which satisfy the abovesaid conditions (1) and (2) at the same time are very few; namely, there are known only two or three combinations such as sapphire (molten liquid) and molybdenum and tungsten (die), silicon (molten liquid) and graphite (die), and so forth. In particular, in connection with chemically active molten liquids of halides other than oxides, it is very difficult to find a combination of materials of the die and the molten liquid which meet with both the abovementioned requirements (1) and (2).
A second shortcoming of the EFG method resides in that the melting of the raw material in the crucible and the temperature control of the upper end portion of the die for growing the single crystal in an optimum condition must be performed by a single heater. In the EFG method, the molten liquid is supplied to the upper end portion of the die through utilization of the rise of the molten liquid by the capillary action, but usually the rise of the liquid by the capillary action is not so large. Accordingly, the upper end portion of the die is not spaced very far apart from the molten liquid level, so that difficulties are encountered in controlling the temperature of the upper end portion of the die independently of the influence of the raw material melting heater. The most serious defect which results from using the single heater both for controlling the temperature of the upper end portion of the die and for melting the raw material lies in that the diameter of the heater is too large to provide a steep thermal gradient on the upper end portion of the die. The upper limit of the growing rate of the single crystal depends on the cooling rate of the molten liquid and, for raising the cooling rate, it is indispensable to make the thermal gradient in the vicinity of the solid-liquid interface steep. In the EFG method, however, it is difficult to provide a steep thermal gradient in the neighborhood of the solid-liquid interface, and consequently a high growing rate cannot be expected.
Still another defect, which accompanies the use of the rise of the molten liquid by the capillary action for the molten liquid supply as in the EFG method, is a fact that the amount of the molten liquid supplied to the solid-liquid interface is substantially determined unequivocally by the properties of the die and the molten liquid in principle. Accordingly, in a case of manufacturing a crystal that is large as compared with the diameter of the capillary tube employed for supplying the molten liquid, or for growing a crystal at a high growing rate, the limit of the growing rate is determined by the amount of molten liquid supplied before reaching the limit of the growing rate dependent on a thermal equilibrium condition which is determined by the cooling rate.